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Re: Tuning system response degradation under heavy ext3/2 activity.

"Liebster, Daniel" <Daniel Liebster adeccona com> wrote:
> When we run any kind of process (especially tar for some reason) that
> creates heavy disk activity the machine becomes Very Slow, (e.g. takes
> 30-45 seconds to get a reply from ls at the console, or a minute to log
> in.)

Linux has traditionally been very bad at handling concurrent disk read and
write traffic - it allows the write stream to starve the reads.  

Fixes for this are still under development in 2.5, alas.

I'd expect that you would see much better behaviour from Andrea Arcangeli's
kernels - he has done quite a bit of work on this problem and when I did
some not-extensive testing on it a couple of months ago it behaved well.

The stalls which you are seeing do appear to be unusually large and
obtrusive.  There may be other factors at play here, such as (perhaps)
over-aggressive queueing in the controllers or really poor bandwidth.

What writeout rate do you actually see?

	time (dd if=/dev/zero of=foo bs=1M count=512 ; sync)


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